I. Many Manichæans have been discovered in Rome.
We call you to a share in our anxiety, that with the diligence of shepherds you may take more careful heed to your flocks entrusted to you that no craft of the devil's be permitted: lest that plague, which by the revealing mercy of the Lord is driven off from our flocks through our care, should spread among your churches before you are forewarned, and are still ignorant of what is happening, and should find means of stealthily burrowing into your midst, and thus what we are checking in the City should take hidden root among you and grow up.
Our search has discovered in the City a great many followers and teachers of the Manichæan impiety, our watchfulness has proclaimed them, and our authority and censure has checked them: those whom we could reform we have corrected and driven to condemn Manichæus with his preachings and teachings by public confession in church, and by the subscription of their own hand, and thus we have lifted those who have acknowledged their fault from the pit of their iniquity by granting them room for repentance. A good many, however, who had so deeply involved themselves that no remedy could assist them, have been subjected to the laws in accordance with the constitutions of our Christian princes, and lest they should pollute the holy flock by their contagion, have been banished into perpetual exile by public judges.
And all the profane and disgraceful things which are found as well in their writings as in their secret traditions, we have disclosed and clearly proved to the eyes of the Christian laity that the people might know what to shrink from or avoid: so that he that was called their bishop was himself tried by us, and betrayed the criminal views which he held in his mystic religion, as the record of our proceedings can show you. For this, too, we have sent you for instruction: and after reading them you will be in a position to understand all the discoveries we have made.
Source: Letters (New Advent)